Effects of inclusion size and orientation on rolling contact fatigue crack initiation observed by laminography using ultra-bright synchrotron radiation

Abstract

The rolling contact fatigue (RCF) tests were performed on a high-strength steel by a newly developed compact rolling contact fatigue test machine, and the formation and propagation of cracks were observed by the synchrotron radiation computed laminography (SRCL). An increase in the sulfur concentration, i.e., increase in inclusion length, resulted in an increase in the variation of flaking life, and materials with horizontal inclusion showed large variation compared to those with vertical inclusion although average flaking lives are almost identical. In the flaking process, cracks, those were perpendicular to the rolling surface and rolling direction, first formed from an inclusion that was adjacent to the rolling surface. Then, the crack propagated in the depth direction. After the vertical crack propagated to a critical depth, a horizontal crack formed, whose face was parallel to the rolling surface. Finally, the horizontal crack propagated to form flaking.